Method of and apparatus for vision testing, etc.



Oct. 20, 1925. I 1,558,348

c. E. FERREE Er A1.

METHOD 0F AND APPARATUS FOR VISION TESTINQ, ETC

Filed Jan. 24,1921 4 sheets-sheet 2' ooooooooooooo oct. zo, 1925. y. 1,558,348

C. E. FERREE ET AL METHOD 0F AND APPARATUS FOR VISIQN-TESTINQ, TC-

Filed Jan. 24,4A 1921 4 Sheets-5h56?. 5

CM.. K

. a RQ www ATTORNEY.

WITNESS." 7% M Oct. 20, 1925.

c. E. F'ERREE Er AL METHOD 0F AND APPARATUS FOR VISION TESTING ETC Filed Jan. 24, 1921 @Siam wmnmE NNN- -OQOOQQOOOGQ ooooooooovooo'oocoqoc moaooocaoooooooooooo @Siem ccmmLsam nue/Mord mi,

W//Uesses Patented Oct.v 20, 1925.

" UNITED STATES PATENT OFFICE.

CLARENCE Elmer.' ummm: AND GERTRUDE RAND FERRER, or BnYN mwa, 'rENNsYLvANIA.

METHOD AND APPARATUS FO'R VISION TESTING, ETC.

Application led January 24, 1921. Serial No. 439,572.

. citizens ofthe United States of America, re-

siding at Bryn Mawr, in the county of Montgomery and` State of Pennsylvania, have invented certainnew and useful Improvements in Methods of and Apparatus for Vision Testing, Etc., ofwhich the following is a specification.

.The objects of our invention or discovery herein lfirst disclosed, shown, described and claimed, is, by our new and limproved method, usually and preferably but not necessarily, carried out andperformed'by a new and improved apparatus, also of'our invention', herein also first disclosed, described and claimed; to accurately test the human.

vision, in practically all its various phases, such for instance as testing the light and the color sense; for testing roughly and minutely acuity of vision under'various degrees of illumination of the object, and determination of the degree of illumination at the thresholdA of'perception of the particular individual eye being tested; and also for testing the eyes in other ways, all as more particularly and at large hereinafter set forth or in other words, our Said new and improved method afnd apparatus. for visional capacities, etc., are each more especially designed and adapted for use in making what are known as eidoptometric, phtoptcmetric,

35 and chromatoptometric visional tests, etc.

And all such three classes of testsare those fitness of individuals for various positions in the military and naval services, especially in the naval and aviation branches thereof. such as pilots, observers, etc., and in many other like fields, in the peaceful arts and 'occupations where the highest visional eiliciency especially when practically instantaneous' perceptive visional acuity, under.

low illuminations is required, to prevent fre;

p quent greatl loss of life and property.

Tov such ends our said new and improved visional testing apparatus, designed and in; 'vented by us, for use. in carrying outJ and performing the said new and improved method of visional testing also 4invented'by us, and preferably but not necessarily used i for carrying out and performing our said method, which apparatus is not by any manner of means limited to such use` inasmuch as the same is adaptable for use for many other purposes in tion, Dand allied arts; all without departing from lthe broad scope of our'said invention. as herein shown, described and claimed; which considered in its broad aspects, comprises a light-projectingapparatus, in which the light-source may be measurably varied the optical, light-projecwithin wide limits; and the projected lightbeam also varied in shape, lsize and intensity, each micrometically measurably indicated by Osuitable index devices; the l'light-beams.

projected illuminating suitable test-letters, or objects, includingvariably adjstably positioned test-objects oGf our invention supported upon a,r suitable variably positioned according to measure indicating index devices at suitable distances from LMthe light-projecting apparatus; and also comprises certain other, land minor mechamsms and appurtenances, hereinaftei screen or support,V

more particularly set forth in the specification and pointedout in the claims; sesses many capabilities, other than those bereinbefore mentioned.

. Our said new and improved apparatus for visional testing together with the manner of operating the same in the carrying out and performing of our 'said new and improved method of visional testing, are-each fully and pos- ,licatiom of which the accompanying drawings form a part, wherein similar letters lor qualities and uses.

l shown and described. in the following specimost essential for determining the visional` numerals of reference designate like orvequivalent parts wherever found thruout'the several views, and in which:

Figure l, is a side-view -in elevation of Aone form of our said vision testing apparatus, used in carrying out and performing our said new andimproved method 'of vision testing, the light projecting apparatus being shown in central vertical longitudinal section, onthe line 1 1, of Fig. 2, looking in the directibn of the arrows; the light rays being transmitted being shpwn by the dotted-lines; and the ,light receiving testingvscreen upon which such light-rays impinge being for clearness shown in perspective as it would appear to a person positioned close to the light-projectin apparatus .on the left hand side thereoi loo ing toward the screen.

Fig. 2, is a top plan view of the apparatus as shown in Fig. 1, the light projector housing being shown in horizont-al section taken on the line 2-2 of Fig. 1.

Fig. 3, is a rear view, on a somewhat larger scale than that of Figs. 1 and 2, of

' the light-transmitting apparatus, taken in I larged scale of the light-projecting tube and' section on the line 3--3 of Figs. 1 and 2, looking in the direction of the arrows.

Fig. 4, is an exterior view of the lightprojecting apparatus housing, llooking toward the left of Fig. 3;

Flg. 5, is a rear view in detail, on an ensmall portion brokenv away at the right) and the top-half in central vertical section;

Fig. 7, is a front end View' of the lightprojecting tube, looking toward the right of ug. 6, with one light-filter in position thereon, and

Fig. 8, is a top-view of the vertical and horizontal light-slit stop-plates shown at the extreme right of Fig. 6, and extreme'front of Fig. 5.

Fig. 9, is a front face view of the calibratlon-chart table, from which is compiled the plotted-curve of the chart shown in Fig. 10;

. which Fig. 10, with its curve, is derived by photometric calibration of one of our' improved visional testing apparatus, machinesor devices, made for the purpose of determining thephotometric characteristics of that particular apparatus.

Referring to the drawings:

The reference letter A,o designatesthe,y

light-projecting apparatus, and B, the screen frame carrying the let-tereidxtest-cards, the

.movable variously positioned test object or objects; and any other test objects to Ybe illumlnated by the projected-light.

` The light-projecting apparatus comprises a housing 11, usually of thin sheet-steel, or other suitable metal, and of the rectangular form shown, having the top central extension 11, carrying `at its center the electriclight socket. 12, in which is supported the electric projection-lamp 13.` The annular wall of the extension 11', is provided with air-holes or perforations 14; and a like line of holes 14', are provided at the bottom of the housing, those at the top having an annular light-shield 15,'andthose at the bottom a like shield 15', suitably located, whereby prevented. As it is essential in order to obtain the hight quality of test results, that the 1i ht transmitted to the test objects for their 1 lumination should be thoroughly diffused-light only,- the housing is provided.

.indicated at 17 ,'which like the walls is lined with opal ground-glass on its interior face, and closes the rear opening in a light tight manner when locked in such closed position, by any suit-able locking device, 17 2;

Firmly secured in position in a suitable circular orifice formed in and thru the front- Wall of the housing is the cylindrical 'projection-tube 18, Within which is supported the focusing-tube 19, provided on the exterior with the downwardly extending rack-gear' 20', meshing with a gear-pinion (not shown) actuated by the milled thumb-nut 21 for reciprocating the focusing-tube 19, in and out of the projection-tube 18, in the well known Way. x g x A lens ring 22 'which carries on its front face the filter-holder or frame 23 is removably secured in known manner upon the outer end of the focusing tube 19. The filter 'holder preferably is of the rectangular open top ped form shown with the slide holding bottom and side-grooves 24 and 24Y (Figs. 6 and 7) usually three in number as shown, into which may be removably successively slipped and supported a variety of different colored or neutral intensity varying glass filter-plates 26. lifted in and out of position bythe upwardly extending handles 26'; or the face plate ofa Nicol prism or otherlight modifier, polarizer, analyzer, etc., by the use of which thelight projected upon the screen and testing objects, may be made of any suitable desired intensity variety, color or tint. i j

Supported securely by the lens-ring 22, at its rear end, but so as to be partially revolubly movable thereon, 4isthe milledits rotation opening and closing, the lightstop iris-diaphragm 28, 'of the well-known 'cards or objects at B, may be varied within large limits; and for convenienceof descriptioir. ysuch iris-diaphragm 28, will be liere- 'l inatter referred to as the stop-diaphragm.

Vthe passage of light out thru such holes is,

edged diaphragm ring 27, carrying and by That the size of the iris light-aperture may be at all times-accurately known, ar-hand or pointer 29, is carried upon the rear face of the diaphragm ring 27, which extends out over a translucent suitably marked indicator scale 30, covering a scale-slot formed in and thru the wall of the focusing-tube 19,

' and extending peripherally vthe length of the rotary path of movement of the diaphragm ring 27, in moving the stop-diaphra m 28,D from the fully open to the fully close positions.

f F ilmly secured in position in any suitable manner upon the rear end of the projection` tube 18, is a frame-ring 31, carrying the peripherally extending back-plate 31', and the inlet diaphragm ring 32, revolubly mounted upon the frame-ring 31, in the same manner as is the diaphragm ring 27, upon the lens-` ring 22, and by its rotary movement-opening and closing the iris-diaphragm 33,

(hereinafter for convenience of'description termed the light inlet-diaphragm in like manner supported therein, and operated from fully open to fully closed position by the rotary movement of the ring 32, such inlet-diaphragm ring 32, being provided on its eriphery with endless-screw gear-teeth mes ing with anendless-screw36, carried by a shaft 36', revolubly supported in journalboxes 37, 37', formed integral with the backplate 34, which shaft 36', extends out thru 'the wall of the housing, and also'thru the equidistant peripheral points on the plate 31', and extending rearward therefrom; and secured upon the outer ends of such studsy by Vposts 41, is the light st-op-plate'34, having the square rectangular central-lightinlet orifice 35, covered by a ground-glassv are respectively" revolub1y supported the li ht-dilusing plate 42, supported at the e ges in any suitable manner on the outer side of 34, so as to wholly cover'the square light inlet orifice whereby by reason of such' ground-glass plate 42, and 'the opal ground-glass inner walls 16, of the housing, the lightprojected will at all times be wholly and' perfectly diffused light.

Formedintegral 'wit the stop-plate 34, or with extensions 43 t ereof, are two vertically alined journal-boxes 44, and 44,'fbeam admitted to the projection-lens L, may' (Figs. 5 and 6) andthe similar horizontally alined journal-boxes 45 and 45', vin which right-and-left-hand threaded screw-shafts -46 and 46'; each of which is held in posin tion against longitudinal movement by washers 47, pinned thereto, or in any other desired manner; the vertical ldouble-screw shaft 46, beingQattached at its upper end to the shaft 48 (preferably of the flexible-form shown) actuated by the hand-crank 48', d

while the like horizontal double-screw shaft 46', is attached to or formed integral with the shaft 49, actuated by the hand-crank 49', bothl of which cranks are exterior to the gear-box 39, (Figs. 2, 3, and 4). i

The upperscrew-thread of the vertical double-screw 46, carries threaded thereon a screw-sleeve 50, and the lower screwthread a like screw-sleeve 50', preferably and usually, as' are all the metallic parts of the light-projecting Aapparatus save the housing,

formed of brass, bronze, monel or other metal, not liable to extreme oxidization; and the screw-sleeve 50, @is formed integral with or firmly otherwise secured to the horizontal upper light? stopplate 51, while the screw-sleeve 50', in like manner carries the lower horizontal light stop-plate 51'. And in substantially similarmanner the vertical Y'lightstop-plates 52 and 52', are connected with the screw-sleeves 53,-and 53', reciprocally moved inward or outward by the ro-f tation of the horizontal double threaded screw-shaft 46, in onel direction `or the other; such vertical butho'izontally reciproca-ble light stop-plates 52 and 52', being usually" and preferably provided unless the same already appears at their vertical outer edges (Figs. 3, 5, -and A8)' bwith the. stitl'ening endbars 54, 54', connected at-the-ir lower ends respectively with the screw-sleeves 53 and 53'; such sleeves, and their respective endbarsv 54 and 54', andtheir stop-plates 52 and 52",' beingusually and preferably` formed -integrallypofbrass, etc., out of one piece of metal.A

As clearly shown in Figs. 3, 5, 6, and 8, the free ends of the horizontal vertically.re` ciprocating light stop-plates 51` and 51' are slidingly supported in a slide-slot or way, 'Y

55h, supported at the ends only' by 'studs' 56a, only one of ,which is shown, formed in- 55a, formed inthe inner face of a guide-bar 55bbetween the upper 'and lower studs56.

In like manner the co-acting vertical light stop-plate 52' is slidablein and outl underneath the screw-sleeves 50 and 50. By this construct-ion and arrangement it will be seen that the character of the-diEused-light be lvaried in shape from that of a most minute square .(made' by bringing the four almost but not quite in contact, at their central meetingedges) to that of an elongated `such Fig. 5) to a complete enlarged square of both the width and verticallength of the orifice 35, made by throwing the plates 51 and 51', backward into their extreme outward positions (indicated in dotted lines in Fig. 5) while the plates 52, and 52', are still in the fully outward possition indicated in j full lines.

If. now it should be desired to have a nonrectangular beam of light projected-upon the screen B, this can be done by manipulating the crank 362, Aso as to turn' the same in the proper direction which thru the endless-screw 36, will turn the diaphragm-ring 32, sou as to gradually close the light-inlet diaphragm 33, in such manner as to first gradually cut ot the corners of the large (or small) square of light beingA transmitted; until the beam becomes a complete circle of any required osize; while at the same time the intensity of the light transmitted (while leaving the beam-image projected of the same size) may' be varied with-v in widelimits either by gradually opening yor closing the stop-diaphragm 28, by rotation of the diaphragm-ring 27 or by mampulation of the illuminatinglamp-rheostatR; by neutral colorless filters of different densities in filter holder, by manipulationl of -Nicol-prism (polarzer and analyzer) in filter holder; or by a combination of opera.-

tion of both R, and 28; or any suitable use singly or collectively of such other devices.

It is highly essential in nearly all cases, and at intervals, especially in the case of making diagnostic tests of persons having progressive optical dieases, to keep accurate record of all the conditions under which suoli several tests have been, made; and for such reason, upon each .of the shafts 48, 4:9 and 36' (Fig. 3), is usually mounted a gearwheel of comparatively small diameter, in-

` dicated respectively by the numerals 55, 56,

and 57, meshing with much larger gearwheels numbered'respectively 55', 56' and 57', all-secured to and' supported upon revoluble shafts 552, 562, and 57 2, which en 'tend out thru the removable wall 60, of the gear-casing (provided to dprotect such gearing from dust, etc.,) an centrally thru a suitable indicating-dial secured vto the outer face of the wall GO, which dials er@ lndl' -upon the screen B; or

(not shown) of suitable type may be used, either alone orl 4upon adjacent dials 553 and 56S4 (usually in millimeters or subdivisions thereof),V respectively the vertical and the4 horizonal, measurements of the variable rectangular light orifice formed by the positioning of plates 51 and 51' and the like horizontally movable and adjustable stop-plates 52 and 52'. In the case of the iris-diaphragm dial 574, the diameter of the iris light-orifice, of the diaphragm 83, at that particular moment is .indicated by the position of the indicator the movable vertically adjustable stop-A hand 574 relative to the dial 573, while in like manner the stop iris-diaphragm 28, immediately to the rear of the projectinglens, has its positional diameter o the lightorifice 28', indicated by the pointer-hand 29 on the illuminated-scale 30.

In all cases the large and small intermeshing4 indicator gear-wheels, are of such tooth-ratios, that there will b e less than a Acomplete revolution of the indicatinghands, etc., to the `full throw of the irisdiaphragm, or the coacting stop-plates 51, 51', and 52, and 52', as the' case may be, from fully open to fully closed positions.

When' it is desired that color and light senseftests should be made, or the test objects viewed by monochromatic light, this is done by inserting proper removable transparent adjustable light filter-plates 26, of the proper color, in the filter-holder` 23, on the outer a'ce of the lens-ring 22, soas to project the light-rays in the proper color upon the test-objects carried thereby; or lneutral absorption screens or filters, singly or in plurality, may be used; or a light-polarizer` or analyzer, the Nicol-prism, or other in combination with the filter-screens; and for the purpose of positionin the plates carrying the Nicol-prism or ot 1er analyser the filter-holder 23, is pro-vided with a plurality of side and bottom holding-grooves, of any suitable plural number (three being shown in Fig. 6,) to receive and-hold suoli y i Adevices in operative position successively or other suitable type, as shown in Fig. 1, andis usually and preferably removably supported in the screen-frame B, having the grooved side standards 61 (Figs. 1 and 2) into which the Snelleu, or other lettered test-card C, may be slipped, and one formsubstitutedofor another at any time; and- Y usually the frame B, is mounted upon a screw or other suitable device base-piece 62, preferably for purposes of stability, of the tripod form shown, the supporting-feet 62 of which are provided with bottoms of felt, (not shown) or other non-i frictional material to permit of the same being moved without friction over the top surface of the supporting table D.

The "light-projecting apparatus housing A, is secured in any desired manner upon a suitable base-plate 64, having a rearward extension 64', upon which is carried,

a suitable rheostat R, and the ammeter N, (Fig. 2) kby which the intensity of the light given by the lamp. 13 is controlled, and the amperage of the current indicated.

The base-plate 64, is provided with4 a downwardly projecting supporting metallic sleeve 65, fitting upon the top of the supporting-standard rod 66, so as to be revoluble thereon, (the sleeve 65, Vbeing provided with a set-screw 65.', for rigidly sec-uring the same against movement when in proper projecting position;o and such rod 66, is reciprocatingly supportedA in vertical position in a table-sleeve 67 secured to the tableD, by a clamp-screw 67; and the rod 66 is provided with a rack 66 on one side by which the same may be raised or `lowered by the rotation of a small pinion or gearwheel meshing with such rack, rotated by a hand-crank 662; a pawl-and-ratchet, set- (not shown) being provided to retain such supportingrod 66, in any required raised position. And formed integral with `the sleeve 67, is a horizontal sleeve 68, in which reciprocates the screen-rod E, upon the outer end of which is connected by a pivot-joint 69 to the forward end of the base-piece or tripod 62 which carriesthe screen-frame B. The screen-frame B may be adjusted to any required angular position relative to the axis of the beam of light projected from A and held in such position by any suitable means, such as a'binding screw; and the screen-rod E, is usually and preferably provided with index-marks in centimeters and millimeters, as indicated at E', of Figs. 1, and 2, showing the distance of the screen-frame B, from the light projectin housing A; the rod E, being secured firm y in any required position in the horizontal slide-'sleeve 68, by means of a set-screw 68. .Revolubly supported by the tripod baseplece 62,.below the test-card C, is our improved rotary test-ob'ect T, which we have found in practice to e far superior to test letters, for` many tests, and also far superior to all known devices for the detection of astigmatisms. While such rotary test object may be of many and various forms and contours, from that of a single bar, pivoted oand the said circle is usually at one end or atthe center, so as -to be capable of being positioned at any required angle to the perpendicular, thru the most minute and micrometric measurements, or of many broken circular or other forms; and one of the many forms' of such rotary test-objects we have found to be of the high-v est eii'iciency, by actual experimentv and prac-M' tical experlmental use, is that of a brokencircle, of an suitable color, in strong contrast with tiie back-ground upon which it is superposed. vIn Fig. 1 a test-object T is shown in the Lform of a jet-black circle upon a brilliant white background. The said circle is broken at the point 7 0 so as to show a white interruption or slot. The said testobject C is mounted or painted upon av revoluble disk of any re uired suitable diameter, say from about ii een to thirty cm. aproximately one-third of the diameter of the said revoluble supporting disk. Thesaid disk is in turn usually and preferably superposed and supported upon a white plate or board 71 supported in the bottom portion of the screen-frame B. The said disk upon which the test-object T is shown isl supported upon a short shaft (not shown) which may be rotated in any suitable and convenient manner. Preferably rotation of said shaft is effected by a flexible'shaft 72. The rear end of the latter is connected with the said shaft and the opposite end thereof/'s connected to the lower end of a short/vertical shaft 73"- to the top end of which is connected the hand crank/73. of the said crank 73 with relation to the indicating dial 74 indicates the posltion of the white interruption or slot 70 of the testobject T. The dial 7 4 is illuminated by light from the lamp 13 which passes 1 nt0 the gearbox 39 through perforations P 1n one of the walls of the lamp housing. It will be under-` stood that the posit-ion ofthe shaft 73 and the dial 7 4 may be changed to any other part of the apparatus as may be found to be convenient and desirable. It is' possible that through wear, twisting of the exible shaft .72, or from some other cause the exact positien of f the interruption or white slot 70,

and exactly indicated upon the dial 74. .n order to test the accuracy of the positionof the test-objectT with respect to the dial 74 it is proposed that an annular degreeor protractor-disk. 76 (see Fig. 1) may be placed temporarily over the disk on whlch the test-object T is mounted or painted. By placing the protractor-disk'7 6 inproper relation with respect to the dial 74 and by then comparing the position of the whlte interruption or slot 70 with the said protractordisk it may be ascertained whether or not the said test-object T is in proper relation to 1,00A The position constituting a test-break, may not be correct- It will be understood that a projecting lens L of any desired size or diameter may be employed but wehave found in the use of the apparatus embodying our invention in actual practice that a lens of 7.5 cm. diameter and of a focal length of 15 cm. is highly efficient and satisfactory. The roject-ion tube, the co-acting and co-ordinatingmechanisms, and the various mechanical parts embodied in the construction of the apparatus should be of appropriate sizes or dimensions as'compared with the diameter and focal length of the lsaid lens. The usual distance of the lframe B, upon which the test-object is supported, from the lens L, is approximately- 81 to 82 cm. although it will be understood that this distance may be substantially decreased or diminished and still permit the kobtaining of efficient test effects.

It will be understood that suitablefilluminating means other than an electric light may be employed. We have found, however, in practice that a well seasoned type C Mazda incandescent electric filament lamp of the round bulb stereopticon form and of 100, 250 or 50() watts capacity, depending upon 'the range of illumination desired, is Well fitted for use in eye testing operations and is of high efficiency.

To form'the calibration-chart shown in Fig. 9, for actuation of the stop-diaphra in 28, to give any re uire'd intensity of lig it, which was derived y photometric measurement from which the plotted-curve chart shown in Fig. 10 was derived, the lamphousing A,was positioned on a photometerbar, at a distance from the photometer head equal to its original distance from the testobject frame B. The scale was then gone over point by point, and the meter-candle value of the light at the photometer-head was measured, and the curve of Fig. 10,l

plotted therefrom.

One great desideratum in vision testing is to be able togra'dually and by minute degrees, vary the size or shape of a testobject, while keeping the illumination constant; or to vary `the illumination, upon a test object of constant size and shape. This new method is provided for, in our new and improved apparatus by varying the size and shape of the light-beam-projecte'd.

This is accomplished by manipulation of the vertical and horizontal light-stop-plates, and of the rear inlet iris-dia hragm 33, adjacent thereto, orby a com ination of mutual adjustments of the two sets of ad justable sto -plates and of such diaphragm 33. In suc case it is preferable to use at `times a plain white, or colored test-'card in place of the printed Snellen or other chart,I and let the projected image formed b the light beam alone serve asthe test o ject.

And by merely having the ghaftsgs, 49Min-d 'n l .white-card, and varied both as to size, in-

tensity of illumination, color, and angular position, thru the widest of ranges; in which case, a suitable crank-actuated shaft, illuminated dial, and connecting mechanism is provided for rotating the stop-plate 34:, for changing the4 angularity of the projected narrow elongated beam of light.

And` it will be seen with our said inii proved apparatus, when the Snellen, or other substantially similar type of test-card having any letters, or 'other test-characters printed thereon, are used; the entire card, or aLsingle line, or a plurality-of lines of letters, or only a single letter or other character, may be illuminated at a time, and the intensity of the lightprojected to illuminate the same, varied from total obscurity, to the highest illumination which the apparatus is capable. of projecting; and Vall this thru micrometrically indicated measureable degrees, which ma be recorded for future reference, diagnosis, study, and comparison.

The testing of' the coloi` sense in terms of the amount of light required to arouse the color sensation is provided for very simply by inserting the appropriate color filters in Athe filter holder 23 and reducing the light intensity to the minimum requirement. Color sense apparatus heretofore and at the present in use seems to be limited to the testing of such gross deficiencies as are' classed as color blindness. Such apparatus is of little use for detectin the.

smaller changes of sensitivity that niar I the advance and recession of many pathological conditions and disturbances. The present apparatus, among other uses, is designed for detecting and measuring any degree of the deficiency and is so far as we know the 'only one that. has been.ofi'ered to the ophthalmologist which is feasible for ofiice work.

One of the chief uses to lwhich, our improved vsional testing apparatus can be put is in the carrying out of our new and improved method of using a variable illumination as a scale, instead of employing a visual-angle scale as heretofore, for determining small difierences in the resolving ower of the eye. Used in this way the illumination scale becomes amplified scale. That is, while the visual angle scale 'stands by definition in a 1 :1 relation to acuity, several divisions of the illumination scale correspon-d to one on the visuall angle scala The sensitivity ofthe illumination scale for detecting small dif? ferences in acuity due to refraction errors is multiplied, therefore, in proportion to this amplification, and this gain in detecting small differences in acuity due to refraction errors is analogous to the gain ion power to detect small differences in the deflection of the magnet system of a galvanometer by means of the amplification accomplished by the use 0f/a tangent scale at a distance of one or more meters.

A Which test principle we consider to be broadly new as to both such method and as to the new and improved apparat-us ydesigned by us for carrying-out such method,u as well as other methods of testing, new and old; all as hereinafter more particularly pointed out in the claims.

One of the chief uses, and valuable features of our visional testing apparatus lies in the accuracy with which, by its use, either in carrying out our new method, or other methods, even slight' astigmatism', may be located and its degree determined.

It is not infrequent to find that in cases of low astigmatism, with the fullillumination of a test-object presenting no smaller gradations in visual angle than are found in the I"Snellen chart, the observer is able to detect no difference in the case or clearness of discrimination of the test character through a range of from 2040 degrees in the placementof the correction. This diiiiculty is especially annoying in the case of children and the unintelligent, untrained and subjective types vof adult. In such cases the apparatus shown here is especially helpful. With it a minimum is left to the comparative and observational powers of the subject. All that he is required to do is to indlcate the position of the test object; that is, in the construction shown, the position of the white interruption or slot y in the test-object` T, the most favorable amount and placement of the correction being determined by the minimum amount of illumination at which he is able correctly to give this indication. o Y

When the e e is fully corrected this minimum should e the same for any meridian into which the-opening in the test object can be turned. The apparatus possesses ample sensitivity, as our results show, for the detection of errors smaller than 5 degrees in the placement of the correction of a low astigmatism or of 0.12 diopter in the amount of the correction.

rotated into the different meridians, the

light is required to discriminate the opening in the circle, could be determined through a series of'settings of the test-object and the light control. The placement of the correction having been determined, its amount could be found by the strength of cylinder required to render the minimum illumination needed vto discriminate the test object the same for all meridians, or more roughly speaking the meridian of the defect and at degrees either way from this position. A quicker method is first to make an approximate determination of the amount and placement of the correction by the clinic methods and employ the illumination meth: od only for a more precise determination. In using this method as a refinement on the clinic methods; the procedure which we ordinarily employ is as follows: The patients eye is fitted with a cylinder of the strength and placement indicated by the clinic tests and the minimum amount of light required to discriminate the opening of the circle is determined in four positions; two in the meridian of the cylinder axis and two in the meridian at right angles to this. If the minima are not equal .in these four posi tions, the cylinder axis is shifted and the determinations are made again; the four positions of the opening of the circle always being in the meridian of the cylinder axisv and the meridian at 90 degrees from it. l If no placement of thecylinder is found which gives equal minima for the four positions,

the strength ofthe cylinder is changed. The strength and place-ment of cylinder which requires both equal and the' smallest amounts of light for the four positions of the test-object is accepted as the final correction. d

By the use of our said new and improved vision testing apparatus, in the carrying out of our new and improved method of vision testing, herein, disclosed, described and claimed, the following results, hitherto and prior to our said invention -or inventions never before obtained in the art of v ision\ obtained,

testing, may be easily and quickly namely: (l) The illumination of the particular test-letter or object being used at the moment, may be varied by micrometrically and photometrically indicated degrees, from the threshold of visional perception llO of either eye of the person under test, up-

ward to the fullest possible illumination, or reversely downward to visinal total disappearance, without any change whatever the colorlvalue of the light so projected.

(2.) Without varying the intensity of illumination, the light may be changed thruout the range of the spectrum. (3) A single `test-letter or test-object may be illuminated eye 'of the test-person; or simultaneously,e

or in sequence the shape ofthe transmitted beam may be varied within wide limits. (4) Acuity of vision at low illuminations, of either eye may be tested, and accurately calibrated, determined; and recorded; for use at future times in making future tests, for determining what, if any, pathological visional changes have occured in the interim. (5) And in like manner the eye vmay be tested for astigmatism, or resolving power, etc., and in like manner calibrated, determined and recorded for like0 use in making future diagnostic tests; and many other capabilities and tests, Vfor almost innumerable other optical determinations, of dia nostic and other character, ma by the use of our said new an improved apparatus for visional testing, not alone'in the carrying out and performing of our new and improved method of visional testing, but in other ways and for almost innumerable other purposes and tests, which will at once suggest themselves to any skilled oculist, opthalmologist, etc., when the necessity therefor arises; all without in any manner departing from the broad scope of the eneric claims hereof either of the metho or the apparatus, so disclosed. f

The resent old and conventional way of using t e visual angle scale for eye testin is to hold the illumination constant an vary the size of the visual angle until the detail can be discriminated. The differences in resolving power are measured and indicated by the smallest value of visual angle .tected and indicated .by the that is required. In our method we hold the visual angle constant and find the lowest or minimum value of illumination that is required to discriminatethe detail. Differences in resolvin power in the different meridians in case o an astigmatism are dedifferent amounts of lightwhich are required just to discriminate the' break in the circle when turned into the different meridiana The advantage of using the illumination scale is lts vastly eater sensitivity for picking up small lerences' 1n resolving power 1n be ma e the different meridians. Differences in resolving power which require so little change in size of visual angle as to be very difcultto measure require larger and easily measurable changes in intensity of illumination.

We could of course, use both scales with our apparatus if we wished. That is we could change either the visual angle or the intensity of illumination or both, by usingV a test-object which is variable in size; as is the projected image of the light-beam from our apparatus here shown; and itlis preferable, when. the elongated light-beam 'is used, and rotated to vdii'lerent meridians,

to place an opaque bar in position over the center of 'the light slit so that there will bc two parallel slits of light; and then both kinds of tests for astigmatismmay be made by turning the light slits to different meridians, namely; first, by keeping the Width )of the light beamsconstant and varying the illumination; or second, by keeping the illumination constant and var ing the width of the beam or beams of lig t. And thus these two forms of tests may be checked one against theother, whereby liability of error will'be reduced to a minimum.

We claim:

1; The method of' 'illuminating uniformly a test chart for the purpose of testing visual ,acuity which com rises the formation of an of constant value at thev eye. I a

3. The method of testing vision for astig-u matism of the e e which comprises the rotation of a test o ject of constant size about its center. as an axis so as to locate a detail thereof in different meridional positions and measuring and comparing the amount of illum'ination required to discriminate said de. ,tail when in such different positions. t 4. The method of testing vision for-.asf certaining the astigmatism of an eye, oo mprising as a step the use of the' illumination scale to detect and indicate differences 1n the resolving power of the eye 1n lts different meridians. 5. The method of ascertaining the meridian and the amount of astigmatism .of an e e` which com rises the determinin for the different meri ians of the eye the iierence in the amount of illumination required to discriminate a detail of constant visual angle in the di'erent meridional positions of said detail.

6. The method of producing upon a screen a colored patch of uniform color and bright ness throughout its entire area for testing the sensitiveness of color vision which comprises the projection of a magnified image r thereby vary the amount of color in said image from obscurity /to full saturation.

7 .v The method of producing upon a screen a colored patch of uniform color and brightness throughout its entire area for testing the sensitiveness of color vision Which comprises the projection ofl a coloredcimage of an evenly illuminated relatively small apeil ture onto a screen and varying and measuring the intensity of illumination of said image from obscurity to maximum illumination to thereby vary the amount' of c olor in said image from obscurity to fulll saturation While maintaining uniformity of illumination in said image throughout its entire area at any moment. A

8. The method of producing upon a screen a colored patch of uniform. color and brightness throughout its entire area for testing the sensitiveness of color vision which com; prises the projection ofa magnified image of an evenly illuminated relatively small aperture onto a screen, interposing a filter plate of selected color in the path of said projected image to impart a selected color thereto, Varying and measuring the intensity of illumination of said image from ob- 'scurity to maximum-illumination to there by vary'the amount of color in' said image from obscurity to full saturation, and simul taneously varying the said aperture -9 The method of producing upon-a screen an illuminated patch of uniform brightness throughout its entire area for testing the sensitiveness of eyes to light Which cemprises the even illumination of an aperture by a light of unvarying character, projecting a magnified image of said aperturevonto a Whitesc'reen, and varying the brightness or said image from obscurity to high intensity.

10. The method of te ting vision for acuity, comprising the illumination of a suitable visional field from complete total obscurity by gradually increasing the illumination by micro-photo-metrically measurable recordable degrees of intensity, and thus determining in minute measurable/,degree the intensity of the -minimum illumination required for the-acuity threshold of the patient being tested, and 'thenreversing the process to determine the degree of illumination at which perception ceases.

11. The method of testing vision, for.

astigmatism, and other forms of ametropia comprising the variable positioning at a plurality of different angles of a movable testobject, and gradually illuminating such testobject in its different angular positions from total obscurity to clear optical perception through microplioto-metrically measurable degrees of intensity.

12. The method of testing vision, for

astigmatism, and other forms of ametropia comprising the projection upon a screen of an elongated light-beam, image and changing the angular position of such light-beam through measured indicated micro-metric degrees of angularity, While varying ,the

light intensity from total `obscurity t'o perfect optical perception micro-photo-metrically 13. The method of testing vision, for astigmatism, and other forms of ametropia comprising the pro'ection upon a screen of an elongated lightearn, and changing the angular position of such ,light-beam through measured indicated micro-metric degrees of angularity, While varying the light intensity from total ception by the patient, by micro-photo-met rically 'measurable degrees, and reversely from optical perception to total obscuration again.

14. The method of testing vision, for astigmatism, and otherforms of ametropia comprising the projection upon a screen of an elongated light-beam, andV changing the angular position of such light-beam through measured indicated micro-metric degrees of angularity, while varying the light intensity from total obscurity to perfect optical perception by the patient by micro-photo-metrically measurable degrees; and simultaneouslyu changing the dimension or dimensions by the patient, by umeasurable degrees.

of the light-beam projected upon the screen.-

15.N The method of testing vision, for astigmatism, and other forms of ametropia 'comprising the projection upon a screen of can elongated light-beam,

angular position of such light-beam through measured indicated micro-metric degrees of angularity while varying the light intensity from total obscurity to perfect optical perception by the patient by micro-photo-metrically measurable degrees, from optical perception to total obscur-ation again; and simultaneously changing the dimension or dimensions of the liglit-beam projectedupon the screen.

16. The method of testing vision, comprising the illumination of a chart carrying suitable test-characters, singly and plurally arranged by projecting a light-beam thereon and varying its intens/ity, so as to succesobscurity to perfect optical perand changing the and reversely sively bring from obscurity to visional perception single characters, any desired plurality of characters; single lines ofcharacters, plural lines of characters, or all the characters carried by the chart. A

' 17. The method of testing vision; comprising the illumination of a chart carrying suitable test-characters, singly and plurally arranged by projecting a light-beam thereon so as to successively bring from obscurity to visional perception, single characters, any desired plurality of characters, single lines of characters, plural lines of characters, or all the characters carried by the chart; the

light-beam image projected upon the screen Ascreen during the use of each particular colored ilter-screen, from total obscurity to complete .visional and color perception,

through measurable, recordable, lmicro-photo-metric degrees.

19. The method of testing visional color perception and other forms of ametropia comprising the projection of a light-beam upon a suitable screen, through ilter-screens of dierent colors or tints, or intensity of colors or tints placed in sequence in the path of the projected light-beam, and simultaneously varying Uthe photo-metric intensity of the light-beam image projected upon the screen during the use of each particular colored filter-screen, from total obscurity to complete visional and 'color perception,

through measurable, recordable, micro-pho.- to-metric degrees, and also simultaneously and in like' manner varying the size, or shape, or both, of the light-image so projected upon the screen.

20. A light-projection apparatus comprising a projection-lens; a housing; an inner surfacing for the housing Walls of light diffusing character; a reciprocable focusingtube supported in the housing Wall carrying the projecting-lensya back stop-plate having a light-inlet-oriiice located Within the casing in axial line with the focusingtube axis; a light source Within said hous-a ing located out of alinement With said tube and orifice, a light-diifusing plate of transparent material covering the light-inlet-orilice of the stop-plate; and mechanism ,forvarying thegshape and size of the light-inletorifice. j

21. A light-projection apparatus comprising a projection-lens; a housing; an inner'surfacing for the housing Walls of light diffusing character; a reciprocable focusingtube supported in the housing Wall carrying the projecting-lens; a back stop-plate having a light-inlet-oriice located Within the casing in axial line with the focusingtube axis; a light-diffusing plate of trans- 'parent material covering the light-inlet-orice of the stop-plate; and manually operable mechanism for varying the light-inletorice, and for simultaneously visually measurably indicating the several dimensions of the light-inlet-orce at the moment. l

22; A light-projection apparatus ocomprising a projection-lens; a housing; an inner Isurfacing foi' the housing Walls of light diiusing character; a reciprocable focusingtube supported in the housing Wall carrying the projecting-lens; a back stop-plate having a. light-inlet-orifice located Within the casing in axial lineI with the focusing-tube axis; a light-diffusing plate of transparent material covering the light-inl'et-oritice 'or' the stop-plate; and manually operable l mechanism for varying the light-inlet-oriice; t'

and means comprising an index or indices for simultaneously visually measurably indicating the several dimensions of the lightinlet-orifices at the moment; the index or indices being illuminated by light from Withinthe housing.

23. A light-projectionapparatus Vcomprising a housing; a projection-lens; a light-diffusing reflecting vlining forming the inner -Wall surface of the housing; a back ,stop-plate having aI light-inlet-orifice 4in line with the axis of the lens located Within4 the housing; and an illuminating-lampv located Within the housing positionedftherein outside of the common axial-line of the projection-lens and the light-inlet-orifice of the stop-plate. 'j

24. A'light-projection apparatus comprising ahousing; a projection-tube located in the Wall ofthe housing; a lens-tube reciprocatingly mounted in the projection-tube; a projection-lens mounted in the lens-tube; an adjustable light-stop iris-diapl'iragm located adjacent to the lens; manually actuated means for moving the light-stopirisdiaphragm from fully closed, to fully open positions; an index-device moved simultaneously With the moving of the light-stop iris-diaphragm indicating at yall timesl the diameter of the light-stop orifice at the moment; a back-plate' having a light-inlet orifice supported at the inner-end of the lprojection-tube; a ground-glass plate carried by the back-plate closing the light-inlet-orifice; two light-stop plates simultaneously movable towardand away from one another in one direction so as to completely clear or close the light-inlet orifice of theback-plate,

supported by the back-plate; two similar light-stop plates simultaneously movable toward and away from one another in a path at substantially a right-angle to the 'path as to completely clear or of the first. mentioned light-stop plates, so close the light-inlet orifice of the back-plate in like manner when so moved; also supported by the back-plate; an adjustable light-inlet-iris-diaphragm carried by the projection-tube located adjacent to the back-plate, adapted when in the fully open position to completely clear the lightinlet orifice of the back-plate; and when in the opposite. position to completely close such light-inlet orifice; manually operated mechanisms for separately actuating the two sets of light-stop plates; like manually operated mechanism for actuating the lightinlet liris-diaphragm; and an illuminated index mechanism for each ot such manually operated mechanisms simultaneously movable therewith measurably visually indicating the position at the moment of the lightinlet, iris-diaphragm, and of the two sets of light-stop plates.

25. A light-projection apparatus comprising a housing; a projection-tube located in the wall of the housing; a lens-tube reciprocatingly mounted in the projection-tube; a

projection-lens mounted in the lens-tube; an adjustable light-stop iris-diaphragm located adjacent to the lens; manually actuated means for moving the light-stop iris diaphragm from fully closed to fully open positions; an index-dcvice moved simultaneously with the moving of the light-stop irisdiaphragm illuminated by the light being projected through the lens-tube, indicating at all times the diameter of the light-stop orifice at the moment; a back-plate having a rectangular substantially square light-inlet orifice supported at the inner-end of the projection-tube; a grouniglass plate carried by the back-plate closing the light-inlet-orifice; two-light stop-plates simultaneously movable toward and away from one another in one direction so as to completely clear or close the light-inlet orifice of the back-plate, supported by the back-plate; plates simultaneously movable toward and away from one another in a path at substantially a right-angle to the path of the first mentioned light-stop plates, so as to completely clear or close the light-inlet orifice of the back-plate in like manner when so moved; also supported by the back-plate; an adjustable light-inlet iris-diaphragm carried by the projectiontube located adjacent tothe back-plate, adapted when in the fully open position to completely clear the light-inlet from one another two similar light-stop orifice of theA back-plate; and when in the opposite position to completely close such light-inlet orifice; manually toperated mechanisms for separatelyv acthating the two sets of light-stop plates; like manually operated mechanism for actuating the light-inlet irisdiaphragm and an illuminated index mechanism for each of such manually operated mechanisms'simultaneously movable therewith measurably Visually indicating the posltion at the moment of the light-inlet irisdiaphragm, and of' the two sets ot' light-stop plates.

26. A light-projection apparatus comprising a-housing; having a. light diffusing refleeting inner wall surface; a projectiontube located in the wall ofthe housing; a lens-tube reciproca'tingly mounted in the projection-tube; an illuminating lamp withini the housing adjacent to the top-wall; a projection-lens mounted in the lens-tube.; an adjustable lightstop iris-diaphragm located adjacent to the lens; manually actuated means for movingl the light-stop iris-diaphragm from fully closed to fully open positions; an index-device moved simulaneously with the moving -of the light-stop iris-diaphragm, indicating at all times the diameter of' the light-stop orifice at the moment; a back-plate having a. rectangular substantially square light-inlet orifice supported at the inner-end of the projection-tube; a ground-glass plate carried by the back-plate closing the light-inlet orifice; two light-stop plates simultaneously movable toward and away from one another in one direction so as to completelyclear or close the light-inlet orifice of the back-plate, 'supported by the back-plate; two similar light-stop plates simultaneously movable toward and away in a path at substantially a right-angle to the path of the first mentioned light-stop plates, so as to completely clear or close the vlight-inlet orifice of the back-plate in like manner when 'so moved; also supported by the back-plate; an adjustable light-inlet iris-diaphragm carried by the projection-tube located adjacent to the back-plate, adapted when in the fully open position to completely clear the lightinlet orifice of the back-plate; and when in the opposite position to completely close such light-inlet orifice; manually operated mechalll.)

nisms for separately actuating the two sets by the said light inlet orifice is uniformly illuminating-lamp; a lamp housing in which 'said illuminating-lamp issituated; a stoplight iris-diaphragm located adjacent to the projection lens in the path of 'the light; a

'back-plate having a light-inlet orifice locatedadjacent to thc lamp. the said lamp being out of alinement with the said lens and the said diaphragm; and means whereilluminated.

28. In a light-projection apparatus, the combination with a projection-lens 'of an illuminating-lamp; a lamp housing in which said illuminatingtlamp is situated; a stop.-

..\ light iris-diaphragm located adjacent to the projection lens in the path ot the light; a back-plate having a light-inlet' orifice located adjacent to the lamp, the said lamp be- -hating-lamp; means tor measurably varying \the illumination transmitted by the lamp; a measurably indicatingly adjustable stop-light iris-diaphragm located adjacent to the projection-lens in the path ot theV light; a back-plate having a light-inlet oriiice located adjacent to the lamp; mechanism for changing the size and shape of the light-inlet orifice to varv in like manner the size Aand shape of the beam of light projected by the lens; and visualfindex indieating mechanism` showing the shape andV size ot' `the-light-inlet orifice at the moment.

30. A light-projecting apparatus, com-l prising an illuminating-lamp; lens; an adjustable light-stop iris-diaphragm located adjacent to the projectionlens; an index indicating the diameter of the iris-diaphragm opening at the moment; `a back stop-light plate havingl a light-inlet slot of a'rectangular elongatede form, and' mechanism for revolubly .moving the back stop-light plate so as to position the lightinlet elongated slot at any required degree o angularity. l

31. A light-projecting apparatus, comrising an 1lluminating-lamp;,a projectionens; an adjustable light-stop iris-diaphragm located adjacent to theprojectionens; an index indicating the diameter of the iris-diaphragm openingfat the moment; a back stop-light plate having a vlight-inlet `slot of a rectangular elon ated form, variable as to its width; an mechanism 'for revolubly movingthe back stop-light plate so as to, position thalight-inlet elongated slot at any required degree of angularlty.

32. In a light-projection apparatus for vision testing, in combination, a projectiona projectionlens, an illuminating-lamp, a lamp house within which said lamp is located, means for providing a light-inlet orifice located4 between the said lamp and the said projection-lens, an image of which -is adapted to be projected by said lens onto a screen, means located betweenthe said oriice and the said projection-lens in-close proximity to the latter for varying the intensity of illumination of the said image while mainc taining uniformity of illumination throughout the extent thereof and also while maintaining the dimensions of said image con-` stant.

33. A vision-testing apparatus comprising Van angle indicating test object of substantially annular form broken at a single point, means 'for supporting said test object, means for rotatably moving said test object into positions with the broken point located at any desired pointv radial to Iits center of rotation, means independent of the light source for varying the intensity of illumination of said test object, and means for measuring and comparing the amounts of illumination necessary to renderl said broken point visually perceptible at its diierent radial positions.

34. A vision-testing apparatus comprising a movable test object which is adapted to be adjusted" `into all angular lpositions in a plane substantially at right angles to the (line of visiuon,.lightprojecting means for illuminating said adjustable test object, and

means for varying and measuring the intensity of illumination of said test object at any moment from extinctionof visual perception upward to full visual perception.

35. In a light-projecting r'apparatus for testing acuity of vision, in combination, a light source, a housing for said light source, a tubular proj ection-lens holder the rear end of which projects into said housing, means for providing a light-inlet opening from said housing into said tubularlprojectionlens holder, which inlet opening is ada ted to be evenly illuminated by the light rom said light source, the said means'including adjustable members whereby the size and shape ot said inlet opening may be varied, a projection-lens mounted in said tubular holder which is adapted to project an image of said light-inlet opening onto a screen,

and means located in close proximity to said said housing into said lens holder, Which inlet to be evenly said light in said tubular holder which is adapted to project an image of said light-inlet open-ing onto a screen, and means located in close proximity to said projection-lens for var ing the intensity of illumination of sald image from obscurity to intense illumina- -tion and at all times maintaining evenness of illumination throughout the entire extent ofthe said image.

Signe-d, at the borough of Manhattan, in the county, city and State this 3rd day of August, 1920.

CLARENCE ERROL'FERREE. GERTRUDE RAND EERREE.

of New York, 

